It is known that a catalyst for the production of methacrylic acid comprising a heteropolyacid compound containing phosphorus and molybdenum is deactivated when the catalyst is used for a long time in a gas phase catalytic oxidation reaction using methacrolein or the like as a raw material, because the catalytic activity the catalyst is reduced due to heat load or the like
As a method for regenerating a deactivated catalyst, JP-A-61-283352 discloses a method comprising the steps of drying a mixture containing a deactivated catalyst, an ammonium ion and a nitrate ion and water, molding the dried mixture and then calcining the molded product in an air stream at 400° C.
JP-A-63-130144 discloses a method comprising the steps of drying a mixture of a deactivated catalyst and aqueous ammonia, dispersing the dried mixture in water, adding a nitrogen-containing heterocyclic compound and an amine or an ammonium carbonate thereto, mixing them, drying and molding the mixture, and then calcining the molded product in an air stream at a temperature of 300 to 450° C.
JP-A-60-232247 discloses a method comprising the steps of dispersing a deactivated catalyst in water, adding a nitrogen-containing heterocyclic compound and nitric acid thereto, mixing them, drying and molding the mixture, heating the molded product in an atmosphere of an inert gas such as nitrogen gas at a temperature of 200 to 600° C. under an atmospheric pressure or a reduced pressure to liberate the nitrogen-containing heterocyclic compound, and then calcining the molded product in an air stream at a temperature of 100 to 400° C.
JP-A-2001-286762 discloses a method comprising the steps of dispersing a deactivated catalyst in water, then adding a nitrogen-containing heterocyclic compound and nitric acid thereto, further adding a compound containing a constituent element disappeared from the catalyst, mixing them, drying and molding the mixture, calcining the molded product in an atmosphere of an inert gas such as nitrogen gas at a temperature of 200 to 600° C., and further calcining the product in an air stream at a temperature of 100 to 400° C.
JP-A-2001-286763 discloses a method comprising the steps of dispersing a deactivated catalyst in water, then adding a nitrogen-containing heterocyclic compound, ammonium nitrate and nitric acid thereto, mixing them, drying and molding the mixture, calcining the molded product in an atmosphere of an inert gas such as nitrogen gas at a temperature of 200 to 600° C., and further calcining the product in an air stream at a temperature of 100 to 400° C.
However, any of the conventional regeneration methods described above does not necessarily recover the catalytic activity or the catalyst life of the deactivated catalyst to a satisfactory extent.